N = gets.to_i
V = gets.split(" ").map{|a| a.to_i}
a = Array.new(N, 0)

a[0] = V[0]
if N != 1
    a[1] = [V[1], V[0]].max
    for i in 2...N
        a[i] = [V[i]+a[i-2],a[i-1]].max
    end
end
puts a[N-1]